In a semiconductor device manufacturing process, a tungsten film is used for filling a recess (via hole) between wirings or a substrate contact recess (contact hole) formed at a semiconductor wafer (hereinafter, simply referred to as “wafer”) that is an object to be processed.
As for a tungsten film forming method, a physical vapor deposition (PVD) method has been conventionally used. However, tungsten W is a high melting point metal and it is difficult in PVD method to deal with a high coverage required along with a recent trend toward miniaturization of devices. Therefore, a chemical vapor deposition (CVD) method capable of dealing with a high coverage and the miniaturization of devices is recently widely used instead of the PVD method. As for the tungsten film forming method using CVD, there is conventionally known a method for allowing reaction between tungsten hexafluoride (WF6) as a source gas and H2 gas as a reducing gas on a wafer, which is expressed by a reaction scheme WF6+3H2→W+6HF. In this case, even a fine hole can be filled with a film with a step coverage of about 100%.
However, along with a recent trend toward a high aspect ratio of a hole, a central portion of the hole may be swollen due to bowing. In this case, even if the step coverage of 100% is ensured, a void or a seam is generated at the central portion of a buried tungsten film. The generated void or seam is exposed by CMP (chemical mechanical planarization) after the film formation, which inflicts adverse effect on semiconductor performance.
As for a technique capable of solving the above problems, there is known a technique in which after a tungsten film is buried, an upper portion of the tungsten film is etched by a plasma of NF3 gas, and then a film is formed to fill a seam in the tungsten film (see Japanese Patent Application Publication No. 2010-153852).
There is also known a technique in which after tungsten W is buried by using H2 gas and WF6 as a film forming gas, a through hole is formed by etching a part of the buried tungsten by using, as an etching gas, WF6 whose flow rate is changed, and then a cavity is filled by forming a tungsten film (see Japanese Patent Application Publication No. 2010-225697).
Further, there is known a technique in which a hole is filled with tungsten W, without generating an overhang, by alternately performing a process of forming a tungsten (W) film in a hole and an etching process using ClF3 gas (see Japanese Patent Application Publication No. 2002-9017).
Furthermore, there is known a technique in which a tungsten film is formed to form a tungsten buried portion in a hole by a CVD method by using WF6 gas and H2 gas, and an opening is formed by etching an upper portion of the buried portion by supplying, as an etching gas, ClF3 gas or F2 gas into a processing chamber that is the same as that used for the film formation, and then tungsten is buried in a void or a seam by forming a tungsten film again by the CVD method in the same processing chamber (see Japanese Patent Application Publication No. 2013-32575).
However, the technique disclosed in Japanese Patent Application Publication No. 2010-153852 is disadvantageous in that the processing is complicated and a throughput is decreased, because a plasma is used for the etching process and a chamber for film formation and a chamber for etching need to be separately provided.
In the technique disclosed in Japanese Patent Application Publication No. 2010-225697, WF6 gas used as a film forming gas is also used as an etching gas, and the etching and the film formation are switched by changing a flow rate of the WF6 gas. However, it is disadvantageous in that the etching property of the WF6 gas is insufficient to make it difficult to reliably perform the etching. Further, such a technique is not enough to deal with miniaturization of devices, because fluorine contained in WF6 inflicts damage to a base film when barrier metal becomes thin along with the miniaturization of devices.
The technique disclosed in Japanese Patent Application Publication No. 2002-9017 prevents generation of a void due to connection of overhang portions by repeating an operation of planarizing a film by performing an etching process when an overhang portion is generated during film formation. Thus, it is disadvantageous in that the processing is complicated and it is difficult to control the processing. Further, etching conditions or the like are not specifically disclosed therein.
The technique disclosed in Japanese Patent Application Publication No. 2013-32575 can solve the problems of the Japanese Patent Application Publication Nos. 2013-32575, 2002-9017 and 2010-225697. However, the technique disclosed in Japanese Patent Application Publication No. 2013-32575 is disadvantageous in that a throughput is decreased in the case of performing the film formation and the etching in the same processing chamber, because a temperature suitable for formation of a tungsten film and a temperature suitable for etching are different.